The present invention relates to adapters for measurement test instrument electrical probes and more specifically to a high density, fine pitch, flexible probe adapter for electronic devices, such as surface mounted integrated circuit devices.
Surface mounted (SMT) integrated circuit devices are fast becoming the dominant type of IC packaging in the electronics industry. These devices come in a wide variety of package configurations and lead pitch geometries. For example, IC packages may be square or rectangular with electrical contact or lead counts from 44 to 232 or higher. A variety of electrical contact or lead types are also being used. Quad flat pack IC's use Gull wing leads or J-leads. Both type of leads extend from the perimeter of the IC package with the former type of leads bending down and outward from the package while the later bend down and fold under the package in a J-shape. The leads are soldered to electrical contact pads formed on a circuit board. Pin-grid-array (PGA) and land-grid-array (LGA) devices have electrical contacts formed in a matrix on the bottom surface of the IC package. The PGA devices have lead wires extending downward that engage a corresponding matrix of through holes in the circuit board. The leads are soldered in the through holes to make the electrical connections. LGA devices have a matrix of raised electrical contacts formed on the bottom surface of the IC, which are soldered to a corresponding matrix of electrical contact pads on the circuit board.
Probing PGA devices with standard measurement instrument electrical probes, such as passive and active oscilloscope probes or the like, requires access to the reverse side of the circuit board on which the PGA device is soldered. For LGA device additional contact pads have to be formed on the circuit board and electrically connected to the matrix of contact pads underneath the LGA device to allow probing of the device.
The small pitch geometries of the quad flat pack SMT devices makes these devices very difficult to probe using oscilloscope or logic analyzer probes. The pitch geometries or lead spacing between leads varies on these device. The most commonly used lead spacings for quad flat packs are 0.65 mm, 0.8 mm, 1 mm, and 0.025 inches. Work is progressing on even smaller pitch geometries in the range of 0.010 inch lead spacing. Using oscilloscope probes on these types of IC packages can cause the shorting of adjacent leads of the device. To overcome this problem, adapters have been developed that provide a transition from the small pitch geometries of the SMT device to a pitch geometry that is compatible with oscilloscope and logic analyzer probes. An example of one such adapter is described in U.S. patent application Ser. No. 07/530,141, filed May 24, 1990, now U.S. Pat. No. 5,166,609, and titled "An Adapter and Test Fixture for an Integrated Circuit Device Package." The adapter has a housing with a top and vertically depending sidewalls that forms an internal cavity for receiving the IC package. Electrically conductive elements are disposed within the sidewalls with one end of the elements making electrical connections with the leads of the IC package. The other end of the elements form electrically conductive pads on top of the adapter. A variety of test heads may be connected to the adapter that have test points with a pitch spacing that allows easy probing with oscilloscope probes and logic analyzer probes.
Current adapters require expensive dies and tooling for each type of package configuration and pitch geometry. Further, positioning accuracy of the adapters, which must fit over the SMT device, is adversely affected by the SMT plastic package itself. The tolerances for the package dimensions are greater than the tolerances for the lead spacings themselves. This can lead to misalignment of the adapter on the device. The only accurate tolerances on SMT devices are the lead pitches themselves.
As SMT devices get larger, heat build-up in the devices becomes a problem. Various types of heat sinks have been mounted on these devices to overcome this problem. However, once a heat sink is secured to a device, a new adapter has to be designed and built to take the heat sink into account. Designing and tooling-up dies for new adapters for each type of device with a heat sink becomes prohibitively expensive.
What is needed is an in-expensive probe adapter for multiple types of IC devices that provides connectivity to standard measurement test equipment electrical probes.